The present invention relates to a power supply device for installation in an apparatus and including a rechargeable battery, and a method for controlling the power supply device.
A power supply device including a rechargeable battery is nowadays often used in various kinds of applications as a power source having superior recycling, economic, and environmental. Specifically, a power supply device including a rechargeable battery is installed in, for example, a hybrid electric vehicle (HEV) using an engine and a motor as a power source. The rechargeable battery is discharged to supply power to apparatuses such as a motor or an air conditioner in the HEV. The motor also functions as a power generator in the HEV. That is, the motor regenerates power when the vehicle is braking or decelerating to charge the rechargeable battery. In this manner, energy, which is released into the atmosphere as heat in a conventional vehicle, is accumulated in the rechargeable battery of the power supply device. This improves energy efficiency and drastically increases fuel efficiency in comparison with a conventional vehicle.
Japanese Laid-Open Patent Publication No. 2000-134707 discloses an example of a power supply device including a cathode side relay and an anode side relay respectively connected to a cathode terminal and an anode terminal of a rechargeable battery. The cathode side relay and anode side relay connect the rechargeable battery and apparatus powered by the rechargeable battery to improve the safety of the power supply device and the apparatus. If abnormal current, such as a short-circuit, flows in the apparatus, the cathode side relay and the anode side relay are switched to an open state to electrically disconnect the apparatus from the rechargeable battery of the power supply device. This prevents abnormal current from flowing into the rechargeable battery. Thus, abnormalities and damage do not occur in the rechargeable battery.
Furthermore, the cathode side relay and the anode side relay include contacts susceptible to fusion resulting from wear or arcs produced during switching operations. When such a fusion occurs, the contact cannot be switched from a closed state to an open state. Therefore, in the prior art power supply device, a fusion checking process is conducted on the cathode side relay and the anode side relay when performing an operation for starting the vehicle to check for abnormalities (fusions) in the cathode side relay and the anode side relay.
The prior art power supply device and relay fusion checking process will now be described in detail with reference to FIGS. 1 and 2.
FIG. 1 is a block diagram showing the structure of a prior art power supply device, and FIG. 2 is a timing chart showing the relay fusion checking process for the prior art power supply device shown in FIG. 1.
The structure of the prior art power supply device will first be described with reference to FIG. 1.
As shown in FIG. 1, the prior art power supply device 1 includes a battery electronic control unit (ECU) 50, which functions as a controller, and a rechargeable battery 51, which includes a plurality of series-connected cells. The prior art power supply device 1 further includes a cathode side relay, which includes a main relay 53 and a precharge relay 55, and a main relay 54, which functions as an anode side relay. The main relays 53 and 54 and the precharge relay 55 each have a first terminal and a second terminal. The first terminal of the main relay 53 is directly connected to the cathode terminal of the rechargeable battery 51, and the first terminal of the precharge relay 55 is connected to the cathode terminal of the rechargeable battery 51 via a resistor 56. The first terminal of the main relay 54 is directly connected to the anode terminal of the rechargeable battery 51.
The second terminal of each of the main relays 53 and 54 and the precharge relay 55 is connected to a motor 52 and a capacitor 57 arranged in a vehicle (apparatus) side. The battery ECU 50 of the prior art power supply device 1 switches the main relays 53 and 54 and the precharge relay 55 between an open state and a closed state to enable or stop the supply of power from the rechargeable battery 51 to the motor 52 and the capacitor 57.
In the prior art power supply device 1, a voltmeter 58 is arranged between the two terminals of the capacitor 57 to measure the voltage of the capacitor 57. The battery ECU 50 uses the charge voltage value of the capacitor 57 measured by the voltmeter 58 to conduct the fusion checking process for the main relays 53 and 54 and the precharge relay 55.
The relay fusion checking process for the prior art power supply device 1 will now be described in detail with reference to FIG. 2.
In FIG. 2, when an ignition key IG arranged in the vehicle side is turned ON at time t1, the battery ECU 50 monitors the output from the voltmeter 58, that is, the charge voltage of the capacitor 57 as the measured voltage Vc. When the measured voltage Vc becomes greater than 0 volts before time t2 at which the precharge relay 55 is switched to a closed state (ON state), the battery ECU 50 determines that the anode side main relay 54 and either one of the main relay 53 and the precharge relay 55 at the cathode side relay are fused.
After closing the precharge relay 55, the battery ECU 50 determines that the anode side main relay 54 is fused if the measured voltage Vc becomes greater than 0 volts before time t3 at when the anode side main relay 54 is switched to the closed state. That is, the fusion checking process of the anode side relay is performed based on changes in the charge voltage of the capacitor 57 between time t2 and time t3 in the prior art power supply device.
Power is supplied to the capacitor 57 by maintaining the precharge relay 55 and the anode side main relay 54 in the closed state. Then, the battery ECU 50 switches only the precharge relay 55 to an open state (OFF state) at time t4 to stop the supply of power to the capacitor 57. The battery ECU 50 stores a measured voltage Vc1 at time t4. The battery ECU 50 maintains only the anode side main relay 54 in the closed state so that discharging occurs from the capacitor 57 toward the motor 52.
Subsequently, the battery ECU 50 closes the precharge relay 55 at time t5 and stores a measured voltage Vc2 acquired at time t5. Further, the battery ECU 50 obtains the difference between the stored measured voltage Vc2 and measured voltage Vc1 to determine that the main relay 53 or the precharge relay 55 at the cathode side is fused when the voltage difference (Vc2−Vc1) is greater than or equal to 0 volts. In other words, the battery ECU 50 determines that the main relay 53 or the precharge relay 55 at the cathode side is fused if the charge voltage of the capacitor 57 rises when maintaining only the anode side main relay 54 in the closed state. In this manner, the fusion checking process of the cathode side relay is performed based on changes in the charge voltage of the capacitor 57 between time t4 to time t5 in the prior art power supply device 1. Afterwards, in the prior art power supply device 1, the battery ECU 50 closes the cathode side main relay 53 at time t6 and then opens the precharge relay 55 at point t7 to start actual power supply to the motor 52.
However, in the prior art power supply device 1, the fusion checking process for the cathode side relay and the anode side relay is performed based on changes in the charge voltage of the capacitor 57 arranged in the vehicle (apparatus) side. Thus, conditions for performing determination during the fusion checking process are dependent on the load of the apparatus. That is, in the prior art power supply device 1, to perform the fusion checking process, at least either one of the precharge relay 55 and the anode side main relay 54 must be closed and at least either one of the cathode terminal and the anode terminal of the rechargeable battery 51 must be electrically connected to the apparatus. Furthermore, the voltmeter 58 must be replaced in accordance with the capacitance of the capacitor 57 or the type of motor 52 connected to the capacitor 57. In particular, if the prior art power supply device 1 is connected to an apparatus that does not have the capacitor 57, an exclusive capacitor must be arranged between the power supply device 1 and the apparatus in addition to the voltmeter 58. Furthermore, the prior art power supply device 1 closes the precharge relay 55 or the anode side main relay 54. Thus, the fusion checking process is performed at different timings for the cathode side relay and the anode side relay.
As described above, the fusion checking process for the cathode side relay and the anode side relay is dependent on the apparatus in the prior art power supply device 1. Further, the fusion checking process is complicated, takes much time, and requires much work.